Because chlorine is so much worse than cholera, typhus, giardia, dysentery ...
Funny how people on private wells drink from them their entire lives without getting any of those things. But the rules do not take into account the source of the water. They only take into account if more than one or two family’s drink from that well. It is those drinking from surface water or recycled water that are at reasonable risk.
There also other ways to treat water without chemicals.
So, now we are supposed to be concerned? Could it be a product of new processes to measure even smaller amounts of chemicals?
The fact one discovers something exists doesn't mean it exists in sufficient concentrations to be lethal in the short term. In the long term, aren't most or maybe all people dead.?